This invention relates to a fuel injection system for single or multiple cylinder internal combustion engines, comprising two fuel injection valves for each cylinder, of which one operates to inject a principal fuel volume, depending upon the engine load, into an induction manifold of an internal combustion engine upstream of an inlet valve, and the other is arranged to inject a secondary fuel volume directly into the combustion chamber in the neighborhood of a spark plug.
The point about internal combustion engines of the specified kind is their low emission of undesirable components in the exhaust gas.
More particularly, for compression ignition engines, systems have already been proposed in which two volumes of fuel are injected in timed succession during each working cycle, but in which -- in contradistinction to the above-specified type -- both volumes are injected into the combustion chamber by a single injection valve. The separation in time of the two injections can be achieved, as is well understood, by stopping the movement of the pump plunger during its delivery stroke and continuing the stroke at a later time, or by contriving the plunger to provide two completely separate fuel deliveries in the course of each working cycle of the internal combustion engine. However, difficulties of a mechanical nature are liable to arise as a result of the high delivery pressures which are required.
A different technique of timely separating the two injections has therefore been proposed, in which each working chamber of the pump is associated with one principal fuel delivery pipe to one of the working cylinders of the internal combustion engine, and a branch pipe delivers a secondary fuel volume to another working cylinder of the engine, throttling means in the branch pipe permitting the volumetric proportion of principal to secondary injection to be controlled. It is again a drawback that the principal and secondary volumes cannot be controlled independently the one from the other. Furthermore, flexibility of control in such injection systems is considerably restricted because the relative timing of principal and secondary injections is fixed by the number and firing order of the several working cylinders of the internal combustion engine.
Another known possibility of effecting sequential injections in a manner based on the last described principle consists in injecting the principal and the secondary fuel volumes into each cylinder through separate valves (German Patent Application No. 1 808 650). The secondary volume can be kept constant by a metering plunger in the supplementary fuel pipe. The defect of this arrangement is that the secondary volume which is delivered via the metering plunger cannot be injected except at pressures below that of the principal volume. This is contrary to the needs of an injection of the secondary volume directly into the combustion chamber, and calls for the use of undesirably high injection pressures for the principal volume. Moreover, with regard to the relative timing of principal and secondary injection the previously mentioned objections also apply. Furthermore, the provision of metering plungers is an added complication and increases cost, besides being an additional source of possible trouble.
Yet another drawback of the known arrangements is that during injection a branched system of pipes is pressurized, a circumstance liable to cause more trouble by the build-up of pressure oscillations.
From the point of view of operating reliability it is a drawback that a defect in one of the pumping elements involves two cylinders at the same time.